Ok so I have a unmoddifyed (really butchered that) jg m4
And I wanted to know if
A- can the regular grips be replaced with the s system grips
B- can any standard ris rail grips be installed to this gun?

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The rail system can only be replaced if you replace the entire upper reciever. The S System does not come apart like a standard M4. Here's what you will need to do this.

Complete upper receiver - must be either metal or plastic to match the lower.

M4 Outer barrel

Deltas Ring

front sight

Hand guard endcap

Upper and lower hand guards

Flash hider

You will need to disconnect the wiring that runs fromt he front of the gearbox intot he S System handguard and remove the fuse assembly.

You can use the same hop and inner barrel assembly and flash hider from your S system.

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